1. Field of the Invention
The present invention relates to a dye-containing curable composition suitable for forming a colored image, which constitutes a color filter used in liquid crystal display devices (LCD) or solid image pickup devices (CCD, CMOS, etc.), as well as a color filter using the dye-containing curable composition, and a process of producing the same.
2. Description of the Related Art
As for processes for producing color filters using a photoresist, the followings have long been known: staining technique comprising pattern formation with a photoresist, followed by pattern staining; electrodeposition comprising formation of a pre-patterned transparent electrode and subsequent pattern formation by ionization of a resin containing pigment dissolved/dispersed in a solvent by voltage application; printing method by offset printing with ink containing thermosetting resin or ultraviolet-curing resin; and pigment dispersing method using a color-resist agent in which a coloring agent such as pigment is dispersed in a photoresist material. Recently major method is the pigment-dispersing method.
Among these processes, in the pigment-dispersing process, a color filter is made by photolithography using a colored radiosensitive composition in which a pigment is dispersed in a variety of photosensitive compositions; this method is advantageous because a pigment used is stable to light or heat. In addition, since the patterning is made by photolithography, highly precise positioning is allowed, and thus the method has widely been utilized as a preferred method in producing a color filter for use in a large-sized and highly fine color display.
Specifically, a colored radiosensitive composition is applied on a substrate by a spin coater or roll coater, and dried to form a film, on which pattern exposure is made and developed to generate colored pixels. This operation is repeated plural times according to the number of hue to give a color filter. For example, these processes are described in JP-A Nos. 1-102469, 1-152499, 2-181704, 2-199403, 4-76062, 5-273411, 6-184482, and 7-140654.
In recent years, the application of color filters has been expanded from liquid crystal display devices (LCD) to solid image pickup devices such as CCDs. In the solid image pickup devices, the pixels tend to become very fine with high density of pickup image, and accordingly it is essential to further reduce the particle size of organic pigment used as a coloring agent for a color filter in the pigment-dispersing method. There is a limitation, however, in the primary particle size of the organic pigment. In order to solve such a problem, it has been attempted to use a dye-type curable composition by incorporating a dye as a coloring agent in the medium of the curable composition in a dissolved state. The method has been described for example in JP-A No. 6-75375.
In recent years, however, much finer particles have been required for the color filter for use in a solid image pickup device, because the so far used pigment dispersion is insufficient to improve the resolution of image and sometimes generates uneven color due to rough particles of the pigment. Thus, the pigment dispersion type was not suitable for the application in the solid image pickup device which requires a color filter having a fine pattern.
In order to solve this problem, the use of dyes has so far been proposed, for example, as described in JP-A No. 6-75375. The curable compositions containing dyes, however, give rise to other problems. That is:
(1) Since conventional pigments are low in solubility in either an alkaline aqueous solution or an organic solvent, it is difficult to obtain a liquid curable composition having a desired spectrum.
(2) Since most of dyes interact with another component contained in the curable composition, it is difficult to adjust the solubility of the curing portion and the non-curing portion (developing properties).
(3) When the molar absorption coefficient (ε) is low, a large amount of dye has to be added, and in such a case other components contained in the curable composition such as a polymerizing compound (monomer), binder, photo-polymerization initiator, and so on have to be reduced; this causes further problems, i.e., decrease of curing power, thermal resistance after curing, and developing properties in the (non)curing portion.
(4) Dyes are in general inferior to pigments in light resistance and thermal resistance.
In addition, when the composition is used in production of color filters for use in a solid image pickup device, the film thickness is required to be in 1.5 μm or thinner particularly differing from the case of using in the production of semiconductors. Therefore, it is necessary to add a large amount of pigment into a curable composition in order to obtain the desired color concentration, resulting in causing the above-mentioned problems.
Because of these problems, it was difficult to satisfy the practically required performance concerning a fine and coloring pattern for a highly fine color filter.
On the other hand, JP-A No. 10-68812 discloses a photosensitive coloring composition in which is used a ternary or multi-element binder containing a monomer having a side chain (meth)acryloyl group, a monomer having an alcoholic hydroxyl group, and a monomer having a carboxylic acid group. This composition, however, has been designed on the assumption that it is applied to the case of using pigments, but there is no description in using dyes soluble in an organic solvent. Moreover, as the ternary or multi-element polymer contains an alcoholic hydroxyl group, it decreases Tg (glass transition temperature) and melt viscosity of the polymer causing a trouble in thermal resistance during patterning. Further improvement is desired, accordingly.